In the conventional local area network system based on a polling/selecting system, the master station carries out a polling on each of the slave stations at all times. Therefore, as the number of the slave stations increased, the time required for the polling process increased in proportion, and it gave rise to the problem that the time required for polling each slave station may be so long that a sufficient polling service to operating slave stations would become impossible, and the overall responsiveness of the system would drop.
To resolve this problem, the present applicant previously proposed a "Polling Device for a Network" (Japanese patent application No. 63-123711). According to this proposal, however, a polling is done even on those stations which may be active but do not require data transmission to be carried out so often, as equally often as those slave stations carrying out frequent data transmission, and unnecessary polling was not sufficiently reduced. In other words, in view of a desire to achieve an efficient utilization of the system, there remains the problem that the unnecessary polling lowers the operating efficiency and impairs the responsiveness of the system.
According to the conventional network based on the token passing system, the token is passed to different data communication devices connected to the network in a sequential manner to avoid the conflict between the data communication devices.
Since the amount of data communication may differ from one data communication device to another, each device may have a different degree of demand for the token. However, according to the system which passes the token from one device to another in a sequential fashion, since the token is passed to all of the devices equally irrespective of the difference in the levels of demand for the token which may exist, those communication devices having a high level of demand for the token receive the token after too long a remission, and the resulting delay in communication time tends to reduce the overall responsiveness of the network.
In the conventional data processing system in which a CPU is connected to an interruption control unit, a DMA control unit and an I/O control unit, the priority levels of the processes carried out by these control units are fixed at the time of system start-up. However, if the priority levels of the processes carried out by different control units are fixed at the time of system start-up, the priority levels may not be optimum depending on the particular contents of the data during the operation of the system. When the priority levels are not optimum, the overall data processing efficiency of the system drops, and the throughput of the system is reduced.
In a computer system consisting of a computer and a plurality of terminals connected thereto, the computer may be operated from each of the terminals within the time period allocated to the particular terminal by the computer. However, according to the prior art, since the timing of allocating time to each of the terminals is uniform without taking into account the skill of the person operating each of the terminals, each of the terminals was not necessarily efficiently utilized, and the efficiency of the overall system was not quite satisfactory.
As hunting methods in an exchange system equipped with the function of a representative number call receiving capability, there is known the determined hunting system according to which a certain priority order of terminals or communication lines is registered in advance and the hunting is always carried out from the head of this priority order, and the distributed hunting system according to which the hunting is always started from the one following the last hunted communication line.
However, according to these conventional hunting systems, depending on the order of registration, it may often occur that non-responsive communication lines are hunted repeatedly and that some of the communication lines may be more hunted than the others even though they may have a same level of responsiveness, so that uneven hunting processes tend to be carried out, and efficient operation of the system is not achieved.